A circuit breaker is a manually or automatically operated mechanical switch that is designed to protect an electrical circuit (e.g., a circuit for a telecommunications application such as a data communications circuit) or an electrical component (e.g., motor, computer, etc.) from damage caused by an overload or short circuit (e.g., fault current). The basic function of the breaker is to detect an overload condition and interrupt current flow. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. Such breaker applications also include telecommunication applications, where the breakers are located at nodal locations typically in a rack system and also remote from each other.
Another device or electrical component that is used to protect from such damage is a fuse. However, a breaker is unlike a fuse which operates once and then must be replaced. A circuit breaker on the other hand is intended to be reset (either manually or automatically) to resume normal operation once it has been tripped.
All circuit breakers have common features in their operation, however, the details can vary substantially depending on the voltage class, current rating and type of the circuit breaker. In general, the circuit breaker must detect am overload condition; in what are termed low voltage circuit breakers this is usually done within the breaker enclosure. The circuit breakers for large currents or high voltages are usually arranged with a pilot device(s) to sense a fault current and to operate the trip opening mechanism. Once a fault is detected, the contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. Once the fault condition causing the tripping of the breakers has been cleared, the contacts must again be closed to restore power to the interrupted circuit.
When the current is interrupted by operation of the breaker, an arc is generated (i.e., between the moving and stationary contacts). Thus, the circuit breaker and its contacts must carry the normal operating load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. The contacts typically are made of copper or copper alloys, silver alloys and other highly conductive materials. The service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current. Consequently, miniature circuit breakers (MCB) and molded-case circuit breakers (MCCB) are usually discarded when the contacts have worn.
In certain type of breakers (e.g., those that in some fashion quench the arc using air), the heat of the arc also can cause a sharp localized increase in air pressure within the breaker's enclosure. Typically the enclosure is designed with exits or ports so the pressurized air resulting from the arc is directed to the ports and so as to exit the enclosure. The breaker and its enclosure can also include other features to facilitate in the quenching of the arc (e.g., arc baffles, compressed air, vacuum, oil, etc.). In addition, such arcing also can create particulate debris.
However, despite these ports and related design features the increased air pressure within the enclosure can cause particulate debris to be dispersed within the enclosure. This can cause fouling of other components in the enclosure which can consequently also shorten the service life of the breaker and thus require an early replacement of the breaker. Pictorial views of magnetic breakers showing such fouling is provided in FIGS. 1A-C.
In addition to tripping during normal operating conditions, breakers undergo a rigorous testing process under overload and/or high interrupt current conditions to assess the operational capability of the breaker as well as assessing the breaker's capability to safely interrupt current flow under extreme conditions. This rigorous testing includes repeated short circuit tests under high current conditions. After initial qualification type testing, the circuit breakers are periodically tested in the same manner to verify continued quality of the breaker manufacture. Because such testing involves repeated testing under overload or short circuit conditions, there is a greater possibility of extensive fouling of components. Such extensive fouling also can lead to an inability of the breaker to be reset during such testing as well as the possibility that the breaker can be rendered inoperable. If the breaker is unable to be reset after tripping during such testing, this could affect the breaker's suitability for use under the desired or intended operating conditions.
There have been attempts to provide a shield or barrier to limit such fouling, however, such attempts have not proven to be completely effective. Referring now to FIG. 2A, there is shown an axonometric view of a magnetic circuit breaker with a standard sear pin trip mechanism which also includes a conventional shielding part that is mounted in proximity to a trip mechanism of the breaker. In the conventional design, the shielding part includes a generally U-shaped member that extends on either side of the trip mechanism and a shield or barrier that extends outwardly from one side of the U-shaped member. In this shielding part design portions of the trip mechanism are not covered by the shielding part.
Referring now also to FIG. 2B, there is shown an illustrative view of the shield/barrier of FIG. 2A that shows the direction of the flow paths of particulate debris and the pressurized air following a tripping or short circuit event. As indicated herein, when the breaker is tripped due to a short circuit event an arc is created causing the creation of particulates and a localized pressurizing of the air with the breaker's enclosure. In the case of the shielding part depicted in FIG. 2A, the pressurized air and particulates flow along and past the right side of the shielding part into the area of the trip mechanism. On the left side, the air is deflected by the sidewardly extending shield/barrier, but is not blocked from passing around the shield/barrier. Thus, the particulates and pressurized air can eventually enter into the trip mechanism area. Consequently, the described shielding part is not sufficiently effective to reduce fouling of the trip mechanism.
It thus would be desirable to provide a new shielding part for a breaker, in particular a magnetic breaker, and methods related thereto. It would be particularly desirable to provide such a shielding part that more effectively shields the trip mechanism from particulate debris resulting from an overload event tripping the breaker in comparison to prior art breakers. It also would be desirable to provide such a shield that can more effectively re-direct air flow from the breaker trip mechanism as compared to prior art devices. Breakers embodying such shield/barriers preferably would improve service life as compared to prior art devices as well as not require the persons maintaining such breakers, to be more highly skilled those servicing conventional breakers.